The present invention relates to a silicone dissolving agent and, more particularly, to a silicone dissolving agent that is thickened to remain in contact with a target silicone film.
Silicone rubbers are used extensively in electronic, construction, and automotive applications. Silicone rubbers have the attributes of solvent and high temperature resistance, and good adhesion properties to a variety of substrates. Silicone resins and rubbers upon curing are cross-linked polymers. Whereas silicone resins often find applications as electrical insulators and water repellant paints and finishes due to exceptional resistance to weather, sunlight, oxidation and high energy radiation, silicone rubbers, such as RTV silicones, most often find applications as seals and gaskets exposed to temperature extremes and limited classes of olefinic solvents.
Single component silicone rubber mixtures commonly used have good shelf lives and vulcanize at room temperature to yield elastomers. These mixtures generally include a polymeric, usually linear siloxane, a cross linker, a plasticizer such as methyl terminated polydimethyl siloxane and optional additives such as curing accelerators, pigments, processing aids and fillers.
Silicone rubbers and resins are labor intensive to remove and replace. Chemical silicone removers have achieved considerable popularity over abrasive methods such as sandpaper abrasive disks, since abrasion modifies substrate dimensions and finish. Additionally, abrasive grit residue often enters fluid circulatory systems and engine components where the silicone served as a sealant or gasket. Chemical silicone removers have generally been strongly acidic or caustic solutions that are not only able to digest cured silicone rubbers and resins, but also attack metallic substrates such as aluminum and steel. Extreme pH silicone removers have a deleterious effect of pitting metallic substrates and damaging wood substrates as well. Solvent swelling using organic solvents such as alkanols, toluene, methylene chloride and the like are capable of swelling a cured silicone rubber or resin yet still require mechanical abrading or scraping to remove the still cured silicone. Further, environmental concerns and the difficulty of maintaining volatile organic compounds in contact with silicone rubber have limited the utility of this method as well.
Silicone removers have become available based upon organosulfonic acid solutions. While organosulfonic acid solutions are effective in digesting cured silicone rubbers and resins, the high volatility and inability to spread thick layers of such a solution onto a silicone rubber or resin have limited the utility of these solutions in automotive and construction applications. Attempts to formulate a viscous silicone rubber or resin remover by mixing a sulfonic acid compound with a polymeric glycol diether and inorganic particulate as exemplified by Japanese published application 2000061390A have met with limited success owing to incomplete silicone matrix dissolution. Thus, there exists a need for a thickened silicone remover that can be applied to various silicone coated surfaces and remain in contact with the silicone until digested, the thickened silicone remover functioning without degrading the underlying substrate.
A silicone dissolving composition includes a sulfonic acid compound, a solvent miscible with the sulfonic acid compound, an organic or organometallic material thickener and sulfuric acid. The solvent is selected to swell a silicone matrix. A silicone dissolving composition is also disclosed including alone or in combination sulfonic acid and phosphinic acid, a solvent miscible with the organo-acid, and a thickener present in a concentration sufficient to maintain the composition in dripless contact with a silicone coated substrate until the silicone is dissolved. The solvent chosen is not only miscible with the organo-acid but also is able to swell the silicone matrix. A silicone film is removed by applying a composition according to the present invention to a substrate coated with a silicone film and allowing sufficient time for the silicone film to be dissolved by the composition.